In recent years, a lithium ion battery, a nickel hydrogen battery, and other non-aqueous electrolyte secondary batteries have, been growing in importance as on-vehicle power sources, or power sources for personal computers and portable terminals. Particularly, the lithium ion battery which is light in weight, and capable of providing a high energy density is expected as the one to be preferably used as an on-vehicle high-output power source. With one typical configuration of this kind of lithium secondary battery, as a separator to be interposed between a positive electrode and a negative electrode, a polyolefin type porous film is used.
However, the polyolefin type porous film is made of a synthetic resin, and hence becomes more likely to be deformed when the temperature increases in the battery. This results in a higher risk of occurrence of the internal short circuit or the like. Therefore, as one of the means for surely preventing the occurrence of a defective condition such as the short circuit occurrence, a study has been conducted on, for example, the formation of a heat-resistant porous layer made of an inorganic filler on the surface of any of a positive electrode, a negative electrode, or a separator (e.g., Patent Literature 1). With this configuration, even when a deformation is caused in the separator, the heat-resistant porous layer can prevent the contact between the positive electrode and the negative electrode, which can inhibit the short circuit occurrence.